(1) Field of the Invention
The present invention relates to a novel process for producing a collagen powder. More particularly, it is directed to a process for producing a collagen powder suitable for use as an additive available for modifying paints, artificial leathers, molding materials and the like, based on synthetic resins such as thermoplastic resins.
(2) Description of the Related Art
Under the present climate of a demand for high quality goods, paints, artificial leathers, molding materials and the like are required to possess a natural leather-like characteric such as appearance, feel, moisture-absorbing and moisture-releasing properties and moisture permeability, and to meet these requirements, attempts to modify these products to obtain a resemblance thereby to natural leathers have been made by adding collagen powders, leather powders, gelatine powders, polyurethane beads and the like to the base synthetic resins for paints, artificial leathers, and molding materials, including polyurethane resins, polyacrylic resin, polyvinyl chloride resins and the like.
Several processes for producing collagen powders and leather powders have been proposed, and most thereof consist only of pulverizing a chromium- or tannin-tanned hide into powder. These raw materials are tanning-treated in the pelt-state, i.e. in the state of a collagen fiber bundle, and therefore even when pulverized, can only be converted into long fibers but not into a fine powder state. As seen in Japanese Examined Patent Publication (Kokoku) No. 40-11075, for example, artificial leathers produced by adding these materials to a thermoplastic resin have a problem in that the resulting leathers have no surface smoothness and thus do not give a natural-leather like feel, although other problems exist. Recently, to solve these problems, a process wherein leather scraps are thermally treated with steam and then pulverized into powder has been proposed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 63-99298, but although the leather powder is in a granular form, since it is heated to 100.degree. C. or more by steam, the powder has a low hygroscopicity and a large apparent bulk density (JIS K 6712), and therefore, when the powder is used as an additive for a paint, for example, a problem arises in that the surface matting and moisture-absorbing and moisture-releasing, properties and the like are very poor.
Furthermore, a process in which a collagen is pulverized into powder, not using leather scrap, has been proposed in Japanese Examined Patent Publication (Kokoku) No. 61-4419. This process comprises carrying out a coarse dispersion, tanning, dispersion, dehydration, and drying treatments, in sequence, using a purified animal pelt to obtain a collagen powder. Nevertheless, since the collagen fiber bundle obtained from the coarse dispersion is tanning-treated, the collagen is changed into the fabric state, and thus this process has a disadvantage similar to that of the process of Japanese Examined Patent Publication (Kokoku) No. 40-11075.
Furthermore, Japanese Patent Application No. 1-217466 proposed a process for producing a wet collagen by pulverizing in water an animal tissue consisting mainly of collagen purified with a special process, and then tanning with a tanning agent. Nevertheless, since the pulverization of the animal tissue in water is carried out at a low collagen concentration of 0.3 to 0.8% by weight, this process has the disadvantages of requiring a long time for the pulverization, and of an insufficient disintegration of the collagen fiber bundle, and thus is incorporated in the powder in the state of a long fabric substance.